1. Field of the Invention
The present invention relates to a feedback operated DC bridge for monitoring voltage variations in a voltage divider circuit used with a voltage controlled resistance component to reach a null balance across the bridge.
2. Discussion of the Background
In order to provide sensor measurements such as temperature, pressure and chemical detection, there is a need for determination of the accurate equivalent resistance of a sensor in response to changes in the environment. Some systems can be modeled as a resistor with the value of the resistor determining the state of the system such as the resistance in a temperature sensor, the piezo-resistance in pressure sensors, or the conductance in a chemical sensor. Thus it is critical to have a resistance transducer that can maintain a stable reading regardless of any noise in the system. Voltage dividers or bridge networks can be used to provide accurate measurements when these systems use resistance sensitive devices. Prior art systems use either a voltage divider approach to determine the value of the unknown resistance or bridge configurations which make use of the off-null signal, V1-V2, to correlate the measurement of an unknown signal transducer 10 as shown in FIG. 1.
Previous bridge measurements require that the off-null signal be equated with the unknown resistance by relationship with the difference voltage or, if the bridge was to be nulled, manual adjustments were required to yield values of the unknown resistance corresponding to settings on a potentiometer that in some cases take several seconds to null.
The prior art systems are sufficient only when the off-null signal remains within a given range and they can be directly correlated with the unknown environmental condition which is being transduced or they are effective when the systems only require a knowledge of whether a signal is above or below a predetermined point. However, when the deviation of the unknown node voltage, V1, is distant from the set point, V2, large gain cannot be used for the off-null signal therefore requiring that the set-point be adjusted or the gain be reduced. Applicants have developed a bridge measurement which addresses this prior art problem.